/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A map which forwards all its method calls to another map. Subclasses should override one or more
 * methods to modify the behavior of the backing map as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingMap} forward <i>indiscriminately</i> to the
 * methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change the
 * behavior of {@link #putAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code putAll} as well, either providing your own implementation, or delegating to the
 * provided {@code standardPutAll} method.
 *
 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingMap}.
 *
 * <p>Each of the {@code standard} methods, where appropriate, use {@link Objects#equal} to test
 * equality for both keys and values. This may not be the desired behavior for map implementations
 * that use non-standard notions of key equality, such as a {@code SortedMap} whose comparator is
 * not consistent with {@code equals}.
 *
 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingMap<K extends @Nullable Object, V extends @Nullable Object>
        extends ForwardingObject implements Map<K, V>
{
    // TODO(lowasser): identify places where thread safety is actually lost

    /**
     * Constructor for use by subclasses.
     */
    protected ForwardingMap()
    {
    }

    @Override
    protected abstract Map<K, V> delegate();

    @Override
    public int size()
    {
        return delegate().size();
    }

    @Override
    public boolean isEmpty()
    {
        return delegate().isEmpty();
    }

    @CanIgnoreReturnValue
    @Override
    @CheckForNull
    public V remove(@CheckForNull Object key)
    {
        return delegate().remove(key);
    }

    @Override
    public void clear()
    {
        delegate().clear();
    }

    @Override
    public boolean containsKey(@CheckForNull Object key)
    {
        return delegate().containsKey(key);
    }

    @Override
    public boolean containsValue(@CheckForNull Object value)
    {
        return delegate().containsValue(value);
    }

    @Override
    @CheckForNull
    public V get(@CheckForNull Object key)
    {
        return delegate().get(key);
    }

    @CanIgnoreReturnValue
    @Override
    @CheckForNull
    public V put(@ParametricNullness K key, @ParametricNullness V value)
    {
        return delegate().put(key, value);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> map)
    {
        delegate().putAll(map);
    }

    @Override
    public Set<K> keySet()
    {
        return delegate().keySet();
    }

    @Override
    public Collection<V> values()
    {
        return delegate().values();
    }

    @Override
    public Set<Entry<K, V>> entrySet()
    {
        return delegate().entrySet();
    }

    @Override
    public boolean equals(@CheckForNull Object object)
    {
        return object == this || delegate().equals(object);
    }

    @Override
    public int hashCode()
    {
        return delegate().hashCode();
    }

    /**
     * A sensible definition of {@link #putAll(Map)} in terms of {@link #put(Object, Object)}. If you
     * override {@link #put(Object, Object)}, you may wish to override {@link #putAll(Map)} to forward
     * to this implementation.
     *
     * @since 7.0
     */
    protected void standardPutAll(Map<? extends K, ? extends V> map)
    {
        Maps.putAllImpl(this, map);
    }

    /**
     * A sensible, albeit inefficient, definition of {@link #remove} in terms of the {@code iterator}
     * method of {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link
     * #remove} to forward to this implementation.
     *
     * <p>Alternately, you may wish to override {@link #remove} with {@code keySet().remove}, assuming
     * that approach would not lead to an infinite loop.
     *
     * @since 7.0
     */
    @Beta
    @CheckForNull
    protected V standardRemove(@CheckForNull Object key)
    {
        Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
        while (entryIterator.hasNext())
        {
            Entry<K, V> entry = entryIterator.next();
            if (Objects.equal(entry.getKey(), key))
            {
                V value = entry.getValue();
                entryIterator.remove();
                return value;
            }
        }
        return null;
    }

    /**
     * A sensible definition of {@link #clear} in terms of the {@code iterator} method of {@link
     * #entrySet}. In many cases, you may wish to override {@link #clear} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    protected void standardClear()
    {
        Iterators.clear(entrySet().iterator());
    }

    /**
     * A sensible implementation of {@link Map#keySet} in terms of the following methods: {@link
     * ForwardingMap#clear}, {@link ForwardingMap#containsKey}, {@link ForwardingMap#isEmpty}, {@link
     * ForwardingMap#remove}, {@link ForwardingMap#size}, and the {@link Set#iterator} method of
     * {@link ForwardingMap#entrySet}. In many cases, you may wish to override {@link
     * ForwardingMap#keySet} to forward to this implementation or a subclass thereof.
     *
     * @since 10.0
     */
    @Beta
    protected class StandardKeySet extends Maps.KeySet<K, V>
    {
        /**
         * Constructor for use by subclasses.
         */
        public StandardKeySet()
        {
            super(ForwardingMap.this);
        }
    }

    /**
     * A sensible, albeit inefficient, definition of {@link #containsKey} in terms of the {@code
     * iterator} method of {@link #entrySet}. If you override {@link #entrySet}, you may wish to
     * override {@link #containsKey} to forward to this implementation.
     *
     * @since 7.0
     */
    @Beta
    protected boolean standardContainsKey(@CheckForNull Object key)
    {
        return Maps.containsKeyImpl(this, key);
    }

    /**
     * A sensible implementation of {@link Map#values} in terms of the following methods: {@link
     * ForwardingMap#clear}, {@link ForwardingMap#containsValue}, {@link ForwardingMap#isEmpty},
     * {@link ForwardingMap#size}, and the {@link Set#iterator} method of {@link
     * ForwardingMap#entrySet}. In many cases, you may wish to override {@link ForwardingMap#values}
     * to forward to this implementation or a subclass thereof.
     *
     * @since 10.0
     */
    @Beta
    protected class StandardValues extends Maps.Values<K, V>
    {
        /**
         * Constructor for use by subclasses.
         */
        public StandardValues()
        {
            super(ForwardingMap.this);
        }
    }

    /**
     * A sensible definition of {@link #containsValue} in terms of the {@code iterator} method of
     * {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link
     * #containsValue} to forward to this implementation.
     *
     * @since 7.0
     */
    protected boolean standardContainsValue(@CheckForNull Object value)
    {
        return Maps.containsValueImpl(this, value);
    }

    /**
     * A sensible implementation of {@link Map#entrySet} in terms of the following methods: {@link
     * ForwardingMap#clear}, {@link ForwardingMap#containsKey}, {@link ForwardingMap#get}, {@link
     * ForwardingMap#isEmpty}, {@link ForwardingMap#remove}, and {@link ForwardingMap#size}. In many
     * cases, you may wish to override {@link #entrySet} to forward to this implementation or a
     * subclass thereof.
     *
     * @since 10.0
     */
    @Beta
    protected abstract class StandardEntrySet extends Maps.EntrySet<K, V>
    {
        /**
         * Constructor for use by subclasses.
         */
        public StandardEntrySet()
        {
        }

        @Override
        Map<K, V> map()
        {
            return ForwardingMap.this;
        }
    }

    /**
     * A sensible definition of {@link #isEmpty} in terms of the {@code iterator} method of {@link
     * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #isEmpty} to
     * forward to this implementation.
     *
     * @since 7.0
     */
    protected boolean standardIsEmpty()
    {
        return !entrySet().iterator().hasNext();
    }

    /**
     * A sensible definition of {@link #equals} in terms of the {@code equals} method of {@link
     * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #equals} to
     * forward to this implementation.
     *
     * @since 7.0
     */
    protected boolean standardEquals(@CheckForNull Object object)
    {
        return Maps.equalsImpl(this, object);
    }

    /**
     * A sensible definition of {@link #hashCode} in terms of the {@code iterator} method of {@link
     * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #hashCode} to
     * forward to this implementation.
     *
     * @since 7.0
     */
    protected int standardHashCode()
    {
        return Sets.hashCodeImpl(entrySet());
    }

    /**
     * A sensible definition of {@link #toString} in terms of the {@code iterator} method of {@link
     * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #toString} to
     * forward to this implementation.
     *
     * @since 7.0
     */
    protected String standardToString()
    {
        return Maps.toStringImpl(this);
    }
}
